x86: Check invalid symbol name

Since bfd_elf_sym_name returns bfd_symbol_error_name for invalid symbol,
name, return error if bfd_elf_sym_name returns bfd_symbol_error_name.

	PR ld/33501
	* elf32-i386.c (elf_i386_scan_relocs): Return error for invalid
	symbol name.
	* elf64-x86-64.c (elf_x86_64_scan_relocs): Likewise.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>